Method and system for facilitating quality of service in edge devices in a fibre channel network

ABSTRACT

One embodiment of the present invention provides a system that facilitates quality of service (QoS) in a Fibre Channel (FC) host bus adaptor (HBA). In this system the bandwidth on an FC link between the HBA and the FC switch can be allocated into a plurality of logical channels, and a respective logical channel can transport data frames of variable length. Furthermore, a respective logical channel is associated with a dedicated buffer. During operation, the HBA communicates to an FC switch the HBA&#39;s capability of receiving or sending a data flow over a logical channel that couples the HBA to the FC switch. The HBA further receives logical-channel allocation information from the FC switch. Furthermore, the HBA associates data frames with a logical channel and transmits data frames to the FC switch on the corresponding logical channel.

RELATED APPLICATION

This application claims benefit under 35 U.S.C. section 119 of U.S.Provisional Patent Application Ser. No. 61/002,252, filed 07 Nov. 2007.

The subject matter of this application is related to the subject matterin the following co-pending non-provisional applications:

-   -   U.S. patent application Ser. No. ______ (attorney docket number        BRCD-112-0377US), entitled “AUTOMATIC ADJUSTMENT OF LOGICAL        CHANNELS IN A FIBRE CHANNEL NETWORK,” by inventors Amit Kanda        and Kung-Ling Ko, filed 12 May 2008;    -   U.S. patent application Ser. No. ______ (attorney docket number        BRCD-112-0378US), entitled “METHOD AND SYSTEM FOR FACILITATING        APPLICATION-ORIENTED QUALITY OF SERVICE IN A FIBRE CHANNEL        NETWORK,” by inventor Amit Kanda, filed 12 May 2008;    -   U.S. patent application Ser. No. ______ (attorney docket number        BRCD-112-0379US), entitled “METHOD AND SYSTEM FOR CONGESTION        MANAGEMENT IN A FIBRE CHANNEL NETWORK,” by inventor Amit Kanda,        filed 12 May 2008;    -   U.S. patent application Ser. No. ______ (attorney docket number        BRCD-112-0393US), entitled “WORKLOAD MANAGEMENT WITH NETWORK        DYNAMICS,” by inventor Amit Kanda, filed 12 May 2008; and    -   U.S. patent application Ser. No. 11/782,894 (attorney docket        number BRCD-112-0208US), entitled “Method and Apparatus for        Determining Bandwidth-Consuming Frame Flows in a Network,” by        inventor Amit Kanda, filed 25 Jul. 2007;        the disclosures of which are incorporated by reference in their        entirety herein.

BACKGROUND

1. Field

The present disclosure relates to Fibre Channel networks. Morespecifically, the present disclosure relates to a method and system forfacilitating quality of service in edge devices in a Fibre Channelnetwork.

2. Related Art

The proliferation of the Internet and e-commerce continues to fuelrevolutionary changes in the network industry. Today, a significantnumber of transactions, from real-time stock trades to retail sales,auction bids, and credit-card payments, are conducted online.Consequently, many enterprises rely on existing storage area networks(SANs), not only to perform conventional storage functions such as databackup, but also to carry out an increasing number of egalitariannetwork functions such as building large server farms.

A predominant form of SAN is the Fibre Channel (FC) network. FCstandards were developed based on High Performance Parallel Interface(HIPPI), a data channel standard developed by Los Alamos NationalLaboratory in the 1980's. HIPPI was designed as a supercomputer IOinterface with high throughput and minimal switching function. As timewent on, optical fiber became cheaper and more reliable, and FC wasdeveloped as a successor to HIPPI to take advantage of the high capacityof fiber optics. FC can carry data channels including HIPPI, SmallComputer Systems Interface (SCSI), and multiplexor channels used onmainframes, as well as network traffic, including IEEE 802, InternetProtocol (IP), and Asynchronous Transfer Mode (ATM) packets. Like HIPPI,the basic topology of an FC network is a star topology with a switchfabric at the center to connect inputs to outputs.

Historically, conventional network appliances (e.g., data-centerservers, disk arrays, backup tape drives) mainly use an FC network totransfer large blocks of data. Therefore, FC switches provide only basicpatch-panel-like functions. In the past decade, however, drasticadvances occurred in almost all the network layers, ranging from thephysical transmission media, computer hardware and architecture, tooperating system (OS) and application software.

For example, a single-wavelength channel in an optical fiber can provide10 Gbps of transmission capacity. With wavelength-division-multiplexing(WDM) technology, a single strand of fiber can provide 40, 80, or 160Gbps aggregate capacity. Meanwhile, computer hardware is becomingprogressively cheaper and faster. Expensive high-end servers can now bereadily replaced by a farm of many smaller, cheaper, and equally fastcomputers. In addition, OS technologies, such as virtual machines, haveunleashed the power of fast hardware and provide an unprecedentedversatile computing environment.

As a result of these technological advances, an FC switch fabric faces amuch more heterogeneous, versatile, and dynamic environment. The limitednetwork functions in a conventional switch fabric can hardly meet thesedemands. For instance, a switch fabric may transport two data flows withdifferent requirements on the same inter-switch link, where one flow isbetween two mission-critical applications and the other is for a simpledata backup. These two flows have different quality of service (QoS)requirements, which are difficult to attain at the same time inconventional FC networks.

SUMMARY

One embodiment of the present invention provides a system thatfacilitates quality of service (QoS) in a Fibre Channel (FC) host busadaptor (HBA). In this system the bandwidth on an FC link between theHBA and the FC switch can be allocated into a plurality of logicalchannels, and a respective logical channel can transport data frames ofvariable length. Furthermore, a respective logical channel is associatedwith a dedicated buffer. During operation, the HBA communicates to an FCswitch the HBA's capability of receiving or sending a data flow over alogical channel that couples the HBA to the FC switch. The HBA furtherreceives logical-channel allocation information from the FC switch.Furthermore, the HBA associates data frames with a logical channel andtransmits data frames to the FC switch on the corresponding logicalchannel.

In a variation on this embodiment, the logical-channel allocationinformation indicates a QoS class to which a respective logical channelbelongs.

In a variation on this embodiment, while communicating to the FC switchthe HBA's logical-channel capability, the HBA initiates a fabric login(FLOGI) process to the FC switch and transmits a vendor-specific datastructure as part of the FLOGI process, wherein the data structureindicates whether the HBA can receive or send data frames over a logicalchannel.

In a variation on this embodiment, the HBA negotiates with the FC switcha buffer-to-buffer credit for a respective logical channel subsequent toreceiving the logical-channel allocation information.

In a variation on this embodiment, prior to receiving thelogical-channel allocation information, the data frames communicated tothe FC switch are transmitted over a default logical channel reservedfor inter-switch communications.

In a variation on this embodiment, the HBA requests port assignment fromthe FC switch. In response to the request, the HBA receives portassignment from the FC switch for a physical device or logical entityassociated with the HBA.

In a further variation, requesting port assignment from the FC switchinvolves sending the request based on an N_Port ID Virtualization (NPIV)process.

In a variation on this embodiment, the HBA transmits a logical-channelquery to the FC switch for information indicating association between alogical channel and a data flow originated from a port within the HBA,wherein the query indicates a source identifier (S_ID) for the port.

In a further variation, transmitting the query to the FC switch involvesaddressing the query to a name server and/or a zone server in the FCswitch.

In a further variation, the query conforms to the format of an ExtendedLink Service (ELS) query.

In a further variation, the query conforms to the format of a FibreChannel Common Transport (FC-CT) query.

In a further variation, the query indicates a destination to which alogical entity corresponding to the S_ID is to communicate.Additionally, the HBA receives from the FC switch an answer whichindicates a logical channel assigned to a data flow from the logicalentity associated to the S_ID and the destination identified in thequery.

In a further variation, the HBA receives, in response to the query, ananswer which indicates a logical channel assigned to a data flow fromthe logical entity associated to the S_ID and a destination that is inthe same zone as the S_ID.

In a further variation, the HBA transmit a logical-channel query to theFC switch for every port within the HBA, thereby allowing data flowsoriginated from different ports within the HBA to be transmitted ondifferent logical channels.

In a variation on this embodiment, the HBA receives an update from theFC switch, wherein the update indicates a change in the associationbetween the logical channels and QoS classes.

One embodiment of the present invention provides a system thatfacilitates QoS in an FC network. During operation, an FC switchreceives a data frame and determines the value of a Class SpecificControl (CS_CTL) filed in the header of the data frame. The FC switchthen associates the data frame with a logical channel based on theCS_CTL value. The bandwidth on an FC link can be allocated into aplurality of logical channels. A respective logical channel cantransport data frames of variable length and is associated with adedicated buffer in the FC switch. The FC then transmits the data frameon the determined logical channel on an outgoing port.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates an exemplary FC network that providesapplication-oriented QoS capabilities in edge devices, in accordancewith an embodiment of the present invention.

FIG. 2 illustrates exemplary virtual channels and data flows, inaccordance with an embodiment of the present invention.

FIG. 3 illustrates an example of providing different QoS to differentdata flows in an FC switch fabric, in accordance with an embodiment ofthe present invention.

FIG. 4 illustrates QoS provisioning to different logical entities withina physical appliance, in accordance with an embodiment of the presentinvention.

FIG. 5 illustrates a conceptual roadmap of QoS provisioning based onvirtual channels, in accordance with an embodiment of the presentinvention.

FIG. 6 illustrates an exemplary use case scenario of virtual channelbased QoS provisioning, in accordance with an embodiment of the presentinvention.

FIG. 7 illustrates another exemplary use case scenario of virtualchannel based QoS provisioning, in accordance with an embodiment of thepresent invention.

FIG. 8 illustrates an example of virtual channel based QoS provisioningin a virtual SAN environment, in accordance with an embodiment of thepresent invention.

FIG. 9 illustrates an example of establishing virtual channels between aswitch and various logical entities associated with a host bus adaptor,in accordance with an embodiment of the present invention.

FIG. 10 illustrates a high-level protocol logic between a host busadaptor and a switch, in accordance with an embodiment of the presentinvention.

FIG. 11 presents a flow chart illustrating an exemplary process ofestablishing virtual channels with differentiated QoS between a host busadaptor and a fabric switch, in accordance with an embodiment of thepresent invention.

FIG. 12 presents a time-space diagram illustrating an exemplary processof establishing virtual channels between logical entities in a host busadaptor and a fabric switch using Fibre Channel Common Transport (FC-CT)queries, in accordance with an embodiment of the present invention.

FIG. 13 presents a time-space diagram illustrating an exemplary processof establishing virtual channels between logical entities in a host busadaptor and a fabric switch using Extended Link Services (ELS) queries,in accordance with an embodiment of the present invention.

FIG. 14 presents a flowchart illustrating an exemplary process of an HBAassigning CS_CTL values to data received from an application, inaccordance with one embodiment of the present invention.

FIG. 15 presents a flowchart illustrating an exemplary process of an FCswitch mapping a data frame to a VC based on its CS_CTL value, inaccordance with one embodiment of the present invention.

DETAILED DESCRIPTION

The following description is presented to enable any person skilled inthe art to make and use the invention, and is provided in the context ofa particular application and its requirements. Various modifications tothe disclosed embodiments will be readily apparent to those skilled inthe art, and the general principles defined herein may be applied toother embodiments and applications without departing from the spirit andscope of the present invention. Thus, the present invention is notlimited to the embodiments shown, but is to be accorded the widest scopeconsistent with the claims.

The data structures and code described in this detailed description aretypically stored on a computer-readable storage medium, which may be anydevice or medium that can store code and/or data for use by a computersystem. This includes, but is not limited to, application-specificintegrated circuits (ASIC), field-programmable gate arrays (FPGA),volatile memory, non-volatile memory, magnetic and optical storage, orother media capable of storing computer-readable media now known orlater developed.

Overview

Embodiments of the present invention facilitate provisioning of QoS inconjunction with virtual channels to the edge devices in an FC network.Particularly, different QoS levels can now be tailored to the needs ofdifferent granularities, such as physical appliances, virtual machines,applications, and sub-application message groups. These new featuresprovide a much more versatile and flexible network environment.Furthermore, the use of virtual channels at edge devices within an FCnetwork allows application oriented QoS provisioning, which has not beenpossible with conventional host bus adaptors and FC switch fabrics.

FIG. 1 illustrates an exemplary FC network that providesapplication-oriented QoS capabilities in edge devices, in accordancewith an embodiment of the present invention. In this example, an FCswitch fabric 100 includes four switch modules, 102, 104, 106, and 108.Each switch module is coupled to a group of network appliances. Forexample, switch module 102 is coupled to a number of servers 110 and anumber of disk arrays 112. A respective network appliance cancommunicate with any appliance (referred to as “target”) in the FCnetwork.

For example, one of the servers 110 can transfer data to and from one oftape backup devices 116. Note that, since the switch modules are notconnected in a fully meshed topology, the data frames transferredbetween servers 110 and tape devices 116 traverse three switch modules102, 104, and 106. In general, the switch modules are coupled byinter-switch links (ISLs), such as ISL 114.

As shown in the example in FIG. 1, large-port-count FC switch fabricsoften include a number of smaller, interconnected individual switches.The internal connectivity of a switch fabric can be based on a varietyof topologies. In this disclosure, the term “switch fabric” refers to anumber of interconnected FC switch modules. The terms “switch module”and “switch” refer to an individual switch which can be connected toother switch modules to form a larger port-count switch fabric. The term“edge device” refers to any network appliance, either physical orlogical, coupled to a switch.

A switch typically has two types of ports: fabric port (denoted asF_Port), which can couple to a network appliance, and extension port(E_Port), which can couple to another switch. A network appliancecommunicates with a switch through a host bus adaptor (HBA). The HBAprovides the interface between an appliance's internal bus architectureand the external FC network. An HBA has at least one node port (N_Port),which couples to an F_Port on a switch through an optical transceiverand a fiber optic link. More details on FC network architecture,protocols, naming/address convention, and various standards areavailable in the documentation available from the NCITS/ANSI T11committee (www.t11.org) and publicly available literature, such as“Designing Storage Area Networks,” by Tom Clark, 2nd Ed., AddisonWesley, 2003, the disclosure of which is incorporated by reference inits entirety herein.

The recent advances in virtual machine software have brought newchallenges to FC networks. Virtual-machine software allows multiplecopies of operating systems to run concurrently on a physical machine,thereby allowing multiple virtual servers to run simultaneously in arelatively isolated manner. Server virtualization allows an enterpriseto allocate different server resources to different application needs.Running virtual servers is a flexible and cost-effective solution,because one can now isolate the consumption of processing power betweendifferent servers and prevent overloaded servers from consuming all thecomputing resources. Furthermore, virtual servers facilitatesoftware-based dynamic load balancing, a desirable feature in modernserver farms.

The virtualization of machines makes an otherwise static FC network moredynamic and unpredictable. For example, when certain virtual servers inthe network are dynamically allocated to handle mission-criticaltraffic, it is important for the FC switches along the data path to givehigher priority to data frames to and from these virtual servers. Inconventional FC networks, such special treatment is not possible,because neither the HBA nor the switch can distinguish data frames fromdifferent virtual servers residing on the same physical machine.

Embodiments of the present invention provide novel mechanisms that allowdifferentiated QoS provisioning to virtual machines running on the samephysical machine. Furthermore, different QoS levels can be associatedwith a large range of logical entities at different hierarchies, e.g.,physical machine, virtual machine, application, and sub-applicationmessage groups. Note that in this disclosure the term “QoS” or “qualityof service” refers to an arbitrary set of service quality parameters. AQoS level or class can be based on an arbitrary number of metrics. Forexample, a given QoS level can specify a guaranteed or best-effort datarate. A more sophisticated QoS level can further specify otherparameters, such as maximum delay and delay variation, maximum dataframe loss rate, and maximum frame misdelivery rate.

In one embodiment, a network appliance's HBA and the FC switch candivide the bandwidth of a physical link into logical channels. Thesevirtual channels can be associated with different priorities withrespect to network resource allocations corresponding to different QoSlevels. The HBA further associates different virtual channels withdifferent applications. Hence, different QoS levels can be guaranteed atthe virtual server, or even the application or sub-application level. Inthe example shown in FIG. 1, each of servers 110 may be running twocopies of virtual servers. Each virtual server may send and receive dataon a separate virtual channel with a given data rate, according to eachvirtual server's service level agreement.

Virtual Channel and QoS

Conventionally, to prevent a target device from being overwhelmed withdata frames, an FC network provides several flow control mechanismsbased on a buffer credit system. A credit represents a device's abilityto accept one frame. A sender maintains a transmission buffer, andretrieves and transmits one frame when a credit is received from thereceiving device. In previous generations of FC switches, each outgoinglink on a switch or HBA is associated with one buffer. This buffer isresponsible for storing data frames from data flows. In this disclosure,the term “data flow” is loosely defined as the data frames flowing froma source ID (S_ID) to a destination ID (D_ID). In conventional FCnetworks, the source ID refers to the outgoing port on the source HBA,and the destination ID refers to the incoming port on the destinationHBA. In this disclosure, however, a source or destination ID can beassociated with a wide range of logical entities, including a physicalappliance (e.g., a physical server) to which an HBA belongs, a virtualappliance, an application, or a sub-application message group.

One problem associated with the conventional buffer configuration isthat it is very difficult to provide different QoS to different dataflows when these data flows are transported on a common link. Forexample, if the receiving device of a data flow is very slow inprocessing the received data frames, the source device is likely toflood the buffers along its data path with its data frames. As a result,other data flows will not be able to use these buffers. Furthermore, thedata frames from the slow flow can cause head-of-the-queue block to thebuffers along the data path, resulting in under-utilization of thenetwork.

One way to solve this problem is to divide the bandwidth in aninter-switch link into logical channels and serve each logical channelwith a separate buffer. This way, different data flows can be assignedto different logical channels and, since each logical channel has aseparate buffer, the data flows can be sufficiently isolated from eachother. Furthermore, a switch can provide different QoS levels to thelogical channels, because it is now possible to implement various bufferscheduling schemes. For example, it is now possible to allocatedifferent guaranteed or best-effort data rates to different logicalchannels or groups of logical channels by using a weighted round-robinscheme when retrieving and transmitting data frames stored in thedifferent buffers.

In one embodiment, such logical channels are also referred to as“virtual channels” or “VCs.” More implementation details of virtualchannels are disclosed in U.S. Pat. No. 7,239,641, entitled “Quality ofService Using Virtual Channel Translation” by Banks, et al., and“Virtual Channels for Switched Fabric” by Martin, et al., available atwww.t10.org/ftp/t11/document.04/04-093v0.pdf, the disclosure of which isincorporated by reference herein in its entirety.

Note that the virtual channel concept in FC networks should bedistinguished from “virtual circuit” (which is sometimes also called“virtual channel”) in ATM networks. An ATM virtual circuit is anend-to-end data path with a deterministic routing from the source to thedestination. That is, in an ATM network, once the virtual circuit for anATM cell is determined, the entire route throughout the ATM network isalso determined. More detailed discussion on ATM virtual circuits can befound in “Computer Networks,” Section 5.6, by A. S. Tanenbaum, 3rd Ed.,Prentice-Hall, 1996.

In contrast, an FC virtual channel is a local logical channel for arespective link between switches. That is, an FC virtual channel onlyspans over a single link. When an FC data frame traverses a switch, thevirtual channel information can be carried by appending a temporary tagto the frame. The allows the frame to be associated to the same VCidentifier on outgoing link of the link. However, the VC identifier doesnot determine a frame's routing, because frames with differentdestinations can have the same VC identifier and be routed to differentoutgoing ports. An ATM virtual circuit, on the other hand, spans fromthe source to the destination over multiple links. Furthermore, an FCvirtual channel carries FC data frames, which are of variable length. AnATM virtual circuit, however, carries ATM cells, which are of fixedlength.

FIG. 2 illustrates exemplary virtual channels and data flows, inaccordance with an embodiment of the present invention. In this example,a switch 210 is coupled to a switch 220 by an outgoing physical link 202and an incoming physical link 204. Each physical link is divided into anumber of virtual channels. For example, link 202 is divided intovirtual channels VC 0, VC 1, . . . , VC n. A respective virtual channelis associated with a buffer dedicated to that virtual channel.Furthermore, a buffer may store data frames from a number of data flows.Correspondingly, a virtual channel can carry multiple data flows.

For example, VC 0 on link 202 is associated with a transmission buffer206 in switch 210. Buffer 206 stores data frames from multiple dataflows, such as data frame 208. Note that in FIG. 2 different frames ofdifferent data flows in buffer 206 are presented with different fillpatterns. FIG. 2 also illustrates a zoomed-in view of the contents of VC0 on link 202. Here VC 0 of link 202 carries four data flows, FLOW 1, 2,3, and 4. Note that these flows may correspond to the same source anddestination or to different source and destination. In other words,although these flows share the same virtual channel on link 202, theymight belong to different end-to-end routes. This is an importantdistinction between FC virtual channels and ATM virtual circuits,because all the data cells in an ATM virtual circuit belong to the samesource/destination pair.

In one embodiment, the VCs on a link can be assigned to different QoSlevels, and the switch can schedule transmission from their respectivebuffers accordingly. For example, among all the VCs on a link, some VCsmay have guaranteed bandwidth, wherein the switch periodically servesthe buffer associated with these VCs to guarantee a minimum data rate.Other VCs may be assigned different weights and participate in aweighted round-robin scheme in transmitting frames in their respectivebuffers. Note that a variety of buffer-scheduling schemes can be used toachieve different QoS results.

FIG. 3 illustrates an example of providing different QoS to differentdata flows in an FC switch fabric, in accordance with an embodiment ofthe present invention. In this example, the physical link betweenswitches 302 and 304 contains a number of VCs. These VCs are groupedinto several QoS classes: Class_F, high priority, medium priority, andlow priority. The Class_F VC corresponds to the Class_F traffic asdefined in the FC standards and carries critical network control andmanagement traffic. In one embodiment, the Class_F VC (or VCs) is servedwith a strict-priority scheduling scheme. The other three QoS classescan use a weighted round-robin scheduling scheme. In one embodiment, arespective VC in the high, medium, and low QoS classes is assigned arelative weight.

In the example in FIG. 3, a data flow 314 is originated from an onlinetransaction processing (OLTP) server 306 and destined for a disk array308. Flow 314 carries mission-critical transaction data, and thereforeis assigned to a VC with high priority. Meanwhile, a second data flow316 is carried on the same physical link. Data flow 316 is between abackup server 310 and a tape backup device 312. Flow 316 is assigned toa VC with low priority, because backup usually does not require the samelevel of latency guarantee as an OLTP transaction. Since each VC has aseparate buffer, flows 314 and 316 can be transported on the samephysical link independent from each other. In other words, even if tapebackup device 312 is slow in processing data frames, data frames fromflow 316 do not interfere with the data transfer of flow 314.

Although the VC configuration illustrated in FIG. 3 can isolate dataflows between switches, a new challenge arises when one physical machineruns multiple virtual machines and produces multiple data flows. Forexample, when OLTP server 306 runs multiple copies of virtual servers ordifferent applications, the data generated by each virtual server orapplication may be of different importance. However, if all the data areco-mingled and share the bandwidth of the link between the HBA of server306 and switch 302, the low-priority data can preempt high-prioritydata. Such a problem exists because conventional HBAs are nothing morethan a network interface card. When the host machine is virtualized, andwhen different applications have different QoS requirements, the limitedfunctions of a network interface card can no longer suffice.

Application Oriented QoS

Embodiments of the present invention allow VCs and different QoS classesto be extended to logical entities with different granularitiesassociated with an HBA. Such logical entities include, but are notlimited to: physical appliances, virtual appliances, applications, andsub-application message groups. A physical appliance can be any physicaldevice that can communicate with an FC switch, such as a server, a diskarray, or a tape backup device. A virtual appliance can be any logicaldevice, such as a virtual machine or a virtual drive. An application canbe any program running on a physical or virtual appliance. Asub-application message group can be any set of data that arecommunicated within an application. For example, the critical financialtransaction data communicated within an e-commerce application can beone message group, while the data exchange for regular browsing can be adifferent message group.

In embodiments of the present invention, VC-based QoS can be extended tothe end points residing with the HBAs. Furthermore, these end points arenot limited to physical entities, but can include any type of logicalentities at different levels. Such extension significantly improves theflexibility of the FC network. With these new capabilities, an FCnetwork can quickly adapt to a dynamic and heterogeneous networkenvironment.

FIG. 4 illustrates QoS provisioning to different logical entities withina physical appliance, in accordance with an embodiment of the presentinvention. The example in FIG. 4 shows how different logical entities,or device objects, can be classified and associated with VCs. In oneembodiment, a network end device has an outer object which is a physicalappliance, such as a physical appliance 404, and which can be referredto by an FC network address (world-wide name or N_Port). Physicalappliance 404 may host one or more virtual appliances, such as virtualappliances 406 and 408, each of which can also be referred to by an FCnetwork address, such as an N_Port ID Virtualization (NPIV) address.Similarly, a virtual appliance may host multiple applications, such asapplications 412 and 414, and a respective application may include manysub-application message groups, such as sub-application message groups416 and 418.

In one embodiment, each level of the logical entities is referred to asobject class. For example, there can be physical-appliance class,virtual-appliance class, application class, and sub-application class.Other definition of object classes is also possible. Each object in anobject class, e.g., a physical appliance, a virtual appliance, or anapplication, can be associated with an individual VC and a QoS class.For example, physical appliance 404 can send data to a QoS enabled SAN402 using VC 422. Meanwhile, virtual appliance 406, application 412, andsub-application message group 416 can each transfer data to SAN 402 viaVCs 424, 426, and 428 respectively.

FIG. 5 illustrates a conceptual roadmap of QoS provisioning based onvirtual channels, in accordance with an embodiment of the presentinvention. From bottom up, the hard capability refers to the hardware's(HBA or switch) capability of receiving and transmitting data frames viaVCs. In one embodiment, the VC-handling capabilities can be implementedin the ASICs of the HBA or switch. Within the scope of hard capability,each VC is regarded as an independent entity.

Above the hard capability, the soft capability allows the hardcapabilities to meet specific customer's business or deploymentrequirements. In one embodiment, the soft capability is divided into twosub categories, soft organization and use restriction. Soft organizationallows the VCs to be logically clustered to form a group (referred to asCluster VCs) or isolates individual VCs that could be assigned tospecific flows or tasks. More specifically, for Cluster VCs, the softorganization allows a set of VCs to be logically clustered. For IsolatedVCs, the soft organization allows reservation of specific VCs that canbe assigned to a group of activities or a single activity.

The use restriction allows Cluster or Isolated VCs to be associated withtheir respective use characteristics: shared or private use. Withrespect to shared use, a VC (Cluster or Isolated) can be used by morethan one flow or more than one transaction type. Generally, a Cluster VCcan be assigned for shared use. With respect to private use, a VC(Cluster or Isolated) can be used by a single flow or message type. Forexample, a host and a target can be assigned to communicate over a VC oftheir own that no other device shares. Generally, an Isolated VC can beassigned for private use.

Once the VC clustering and usage are defined by the soft capability, theflows or tasks can be assigned to the VCs based on the previouslydefined object classification (e.g., physical appliance, virtualappliance, application, sub-application message group, etc.). Themapping of information flow to VCs could be static or be computed atruntime based on business driven policies.

Static mapping refers to predetermined mapping between information flowand VCs. Static mapping is not dynamically computed, and may include twosub-categories: address based assignment and application basedassignment. With address based assignment, a flow is assigned to the VC(Cluster or Isolated) based on network addresses. With application basedassignment, the VCs are assigned based on application types.

With respect to runtime mapping, the VCs are assigned to the informationflow on a per transaction or per message group basis by, for example,frame inspection. An example would be to assign data frames for onlinepurchase orders to a higher priority VC, compared with data frames foraccount summary requests.

FIG. 6 illustrates an exemplary use case scenario of virtual channelbased QoS provisioning, in accordance with an embodiment of the presentinvention. At the hard-capability level, a switch 602 divides thebandwidth in a link into nine VCs. Next, based on a user defined VCconfiguration, the nine VCs are grouped into two VC Clusters and threeIsolated VCs within the switch's soft capability, in accordance with aset of business driven policies. Furthermore, the user can allocateVC-7, VC-8, and VC-9 for private use, whereas VC_CLUSTER-1 andVC_CLUSTER-2 are for shared use.

Subsequently, in the process of application-oriented QoS (AoQ)-basedflow assignment, data flows are mapped to the VCs. In this example, VC-9is dedicated to the traffic between appliance 604 and appliance 606.That is, all the virtual machines and applications hosted by appliances604 and 606 share VC-9. VC-8 is dedicated to the communication betweenapplication 610 and application 614. VC-7 is dedicated to specificmessage group B between application 608 and application 612. Messagegroup A between application 608 and application 612, as well as a numberof additional devices, share VC_CLUSTER-2. Similarly, a number ofdevices share VC_CLUSTER-1.

FIG. 7 illustrates another exemplary use case scenario of virtualchannel based QoS provisioning, in accordance with an embodiment of thepresent invention. In this example, an appliance 700 includes a policyengine 702 and hosts three applications, APP 1, APP 2, and APP 3.Appliance 700 also includes an HBA which manages two VC CLUSTERS andseveral VCs. As illustrated in FIG. 7, application APP 3 communicateswith a target T4 via a dedicated VC 706. Application APP 3 alsocommunicates with application APP Y in an appliance 704 via a shared VC708. Additionally, application APP 2 communicates with application APP Xin appliance 704 via a shared VC 710. Note that VCs 708 and 710 may beshared with other appliances.

Policy engine 702 further maps the communication from application APP 1to target Ti to one of the VCs in VC_CLUSTER-1. The communicationbetween appliance 700 and target T2 is mapped to VC_CLUSTER-2. Policyengine 702 also maps the communication between appliance 700 and targetT3 to shared VC 712.

In one embodiment, private VCs (Cluster or Isolated) could be used in avirtual SAN configuration. FIG. 8 illustrates another exemplary use casescenario of virtual channel based QoS provisioning, in accordance withan embodiment of the present invention. In this example, a virtualswitch fabric can be assigned a private VC_CLUSTER-1 of its own with apredefined, guaranteed bandwidth. The virtual switch fabric andVC_CLUSTER-1 can be dedicated to virtual SAN 802. The rest of the VCsand VC clusters can serve the rest of physical SAN 800.

Extending VC and QoS Capability to HBA

As described above, trends in computer hardware have led to theproliferation of powerful yet relatively inexpensive multiprocessorservers. In many cases, applications do not fully utilize these systems.As recent industry developments such as multi-core processors becomecommonplace, the degree of under-utilization is expected to increase.These realities have led to renewed interest in virtual machines forserver consolidation. Virtual-machine environments provide a softwarelayer that enables users to create multiple independent virtual machineson the same physical server.

By running multiple virtual machines simultaneously, a physical servercan be driven to much higher utilization. Although the underlyingphysical resources are shared, each virtual machine is fully isolatedfrom other virtual machines and executes a separate instance ofoperating system and separate application software. Currently, amajority of virtual machines are FC connected.

As each virtual machine runs as an independent entity, essentiallysharing the same hardware underneath like an FC HBA, it is importantthat these virtual machines have independent FC addresses. The HBAvendors have started to use NPIV for isolating the sessions for eachvirtual machine. For example, a respective virtual machine can beassociated with a fixed port world-wide name (WWN), which is migratedwhen the virtual machine is moved from one server complex to another.

Since a conventional HBA has only one link to the switch without any VCcapabilities, two virtual machines residing in the same physical servercould suffer from network congestion incurred on the link between theHBA and the switch. For example, if one virtual machine's target isslow, that virtual machine's data frame would quickly saturate thebuffer in the HBA, which is shared with the second virtual machine. As aresult, the second virtual machine would starve for bandwidth.

In previous generations of FC products, the VC concept is not extendedto the virtual machines and HBAs. The VCs are assigned to a flow only atthe ingress of a switch, i.e., at the F_Port or FL_Port coupled to anHBA. Embodiments of the present invention facilitate the extension ofVCs and VC-based QoS to HBAs and the logical entities associated withHBAs. As a result, the data flows from different logical entities can besufficiently isolated from each other within the HBA, which helpsprevent network congestion and unfairness.

In embodiments of the present invention, the HBA can negotiate andextend the VCs into the fabric. In general, the HBA can associate eachNPIV address with a VC. The HBA can also associate data frames withdifferent VCs based on the CS_CTL field in the data frame's FC header.Furthermore, embodiments of the present invention do not require anydirect user configuration of the HBA. With respect to data flows fromthe HBA to the switch, the switch's F_Port can be in a pass-throughmode, where the VC index is retained for the data frame. In other words,the VC associated with a data flow can be set at the HBA and goes allthe way to the destination device. With respect to data flow from theswitch to the HBA, the VC identifier in a data frame is retained by theswitch before the data frame is transmitted to the HBA.

FIG. 9 illustrates an example of establishing virtual channels between aswitch and various logical entities associated with a host bus adaptor,in accordance with an embodiment of the present invention. A physicalserver 904 includes an HBA 916 and hosts two virtual servers 905 and914. During operation, HBA 916's physical port 920 logs into a switch902 and receives an N_Port address. In addition, virtual server 905 andvirtual server 914 receive their respective NPIV port addresses fromswitch 902. For example, virtual server 905 has a virtual NPIV port 922which can communicate with switch 902 via a VC. Similarly, virtualserver 914 has a virtual NPIV port 924. Applications 906 and 912, andsub-application message groups 908 and 910, can communicate with HBA 916via NPIV port 924. In one embodiment, HBA 916 can assign different VCsto the data from different applications and sub-application messagegroups by inspecting the payload in the data frames (i.e., “sniffing”the payload data). This way, any logical entity associated with HBA 916can have an independent NPIV port and a VC to communicate with switch902. Other VC dispatching mechanism can also be used by HBA 916.

FIG. 10 illustrates a high-level protocol logic between a host busadaptor and a switch, in accordance with an embodiment of the presentinvention. In general, an HBA 1002 first establishes the VCs with aswitch 1004. To do so, HBA 1002 can perform the fabric login (e.g.,FLOGI) and VC negotiation with switch 1004 by communicating withwell-known addresses (WKAs) in switch 1004 (such as 0xFFFFFE and0xFFFFFD) (operation 1006). HBA 1002 can then query switch 1004 forVC-to-flow mapping by communicating with WKA 0xFFFFFC in switch 1004(operation 1008). Subsequently, when there is a QoS or VC configurationchange, switch 1004 can report a VC-to-flow mapping change to HBA 1002(operation 1010).

FIG. 11 presents a flow chart illustrating an exemplary process ofestablishing virtual channels with differentiated QoS between a host busadaptor and a fabric switch, in accordance with an embodiment of thepresent invention. During operation, the HBA first detects its VCcapabilities (operation 1102). The HBA then performs login to a switchand reports its VC capabilities (operation 1104). Next, the HBAnegotiates the buffer-to-buffer credits for each VC (operation 1106).The HBA further queries the switch for VC-to-flow mapping for each NPIVport associated with the HBA (operation 1108). Subsequently, the HBA canbegin forwarding and receiving regular payload data frames for differentlogical entities (operation 1110).

In general, after the HBA receives its network address, it can fetch theVC-to-flow mapping. After the FLOGI procedure (and FDISC if NPIV is usedfor multiple logical entities), the HBA learns the D_IDs of all thelogical entities. In order to compute the flow, the HBA is expected toknow the D_ID with which each of its NPIV addresses plans tocommunicate. For each possible flow, the HBA learns from the switch theproper VC identifier. In one embodiment, the HBA determines theVC-to-flow mapping by sending a query to the switch's name server and/orzone server. In response, the switch's name server replies to the HBAwith VC identifiers associated with the flows specified in the query.

Ideally, the HBA queries the VC-to-flow mapping before anyapplication-level communication starts. An HBA may have multiple FCaddresses due to the use of NPIV for logical entities. In oneembodiment, every time the HBA solicits an FC address from the switch byperforming a FLOGI or FDISC procedure, the HBA queries the switch forVC-to-flow mapping information for that FC address. The HBA may optimizethe query by specifying multiple addresses in that query. Note thatthere is no restriction as to how the HBA queries for the VC-to-flowmapping information. Furthermore, it is assumed that theapplication-level communication starts when an FC address in the HBAsends a port login (PLOGI) sequence to a non-WKA address in the switch.

There are at least two ways to implement a VC-to-flow mapping query: inthe form of an Extended Link Service (ELS) query to WKA 0xFFFFFC, and inthe form of a Fibre Channel Common Transport (FC-CT) query to theswitch's name server. The advantage of an ELS query is that it does notrequire any overhead associated with PLOGI and PLOGI_ACC. The advantageof a name server FC-CT query is that it is in line with other forms ofqueries that are performed with the name server. In either case, thepayload of the query and response shall be similar. For the sake ofsimplicity, assume that the query is denoted as QoS_QUERY, whether it isan ELS query or an FC-CT query.

In one embodiment, the QoS_QUERY is sent separately for each NPIVaddress. The QoS_QUERY can be sent from the S_ID of the NPIV address tothe name server at WKA 0xFFFFFC. A second QoS_QUERY can then be sentfrom the S_ID of another NPIV address. The QoS_QUERY can indicate one ofthe two modes (Flow Mode and Source Mode) in which the HBA expects themapping to be. In the Flow Mode, the QoS_QUERY specifies the WWN or D_IDof each destination with which the S_ID of the QoS_QUERY (that is, theNPIV address of the source logical entity) plans to communicate. In theSource Mode, the switch returns the VC for each D_ID that is in the samezone as the S_ID of the QoS_QUERY.

The name server on the switch then sends a response back to the HBA. Theresponse associates a VC with each WWN/D_ID specified in the QoS_QUERYif it is in the Flow Mode. It is possible that the QoS_QUERY may containWWNs or D_IDs not known to the switch. In that case, the switch canreturn a Not Known value for such WWNs or D_IDs. Later, if there is achange to the VC configuration, zone configuration, or QoS configuration(e.g., flow-to-VC mapping), the switch can send a Registered StateChange Notification (RSCN) to the HBA, following which the HBA canresend the QoS_QUERY to the switch.

FIG. 12 presents a time-space diagram illustrating an exemplary processof establishing virtual channels between logical entities in a host busadaptor and a fabric switch using Fibre Channel Common Transport (FC-CT)queries, in accordance with an embodiment of the present invention.During operation, subsequent to the HBA obtaining its FC address(operation 1206), the HBA initiates a PLOGI process on VC-0 which is forClass_F traffic (operation 1202). In response, the switch sends anacceptance PLOGI_ACC (operation 1204). Subsequently, the HBA sends aQoS_QUERY as an FC-CT query to the name server (operation 1206). Theswitch then sends a response (operation 1208). Subsequently, the HBAsends a logout request (operation 1210). In response, the switch sendsback a logout acceptance (operation 1212).

FIG. 13 presents a time-space diagram illustrating an exemplary processof establishing virtual channels between logical entities in a host busadaptor and a fabric switch using Extended Link Services (ELS) queries,in accordance with an embodiment of the present invention. Duringoperation, after the HBA has received an FC address (operation 1301),the HBA sends an ELS QoS_QUERY on VC-0 to the switch (operation 1302).In response, the switch sends an ELS response with the VC-to-flowmapping information with respect to the S_ID in the QoS QUERY (operation1304).

CS-CTL Based VC Assignment

The Class Specific Control (CS-CTL) field in an FC frame headerindicates a desired priority for the frame when the frame's prioritybit, bit 17, in the F_CTL field of the FC header is set to “1.” In oneembodiment, the system does not require the HBA to negotiate VCs withthe switch. Instead, the ingress switch is responsible for mapping dataflows to VCs based on the CS-CTL field in the data frames.

Some applications, such as the Work Load Manager in mainframe computers,can pass priority information to the HBA. The HBA can then map suchpriority information to the CS_CTL values in the FC frames. When theframes enter the ingress port on an FC switch, the switch can beprogrammed to map different CS_CTL values to VCs.

Note that CS_CTL-based VC assignment can implement all the functions ofin-band priority and allow applications to control the VC or QoS classto be associated with the data flows. However, since the HBA is notrequired to have VC capabilities, data flow isolation may be difficultto attain, and congestion between data flows originated from differentvirtual servers may still occur on the link between the HBA and theswitch.

FIG. 14 presents a flowchart illustrating an exemplary process of an HBAassigning CS_CTL values to data received from an application, inaccordance with one embodiment of the present invention. Duringoperation, the HBA receives data from an application (operation 1402).The HBA then determines the priority information of the received data(operation 1404). Note that the application may set the priority for thedata. If such priority information is not explicitly provided by theapplication, the HBA may maintain a set of policies that associatepriorities to different classes of applications. Note that the term“application” is used in a general sense here. An “application” can be avirtual server, an application running on a physical or virtual server,or a sub-application message group. In other words, thepriority-assignment policy maintained by the HBA can associatepriorities with any granularities or hierarchies of logical entitiesthat can communicate via the HBA.

Next, the HBA encapsulates the received data in FC data frames and setsthe CS_CTL value of these data frames based on the determined priority(operation 1406). The HBA then transmits the data frames to an FC switch(operation 1408).

FIG. 15 presents a flowchart illustrating an exemplary process of an FCswitch mapping a data frame to a VC based on its CS_CTL value, inaccordance with one embodiment of the present invention. Duringoperation, the switch receives a data frame from an HBA (operation1502). The switch then determines the value of the CS_CTL field in theframe header (operation 1504). Based on the CS_CTL value, the switchassociates the data frame to a VC based on the CS_CTL value (operation1508). The switch further determines an outgoing port for the data frame(operation 1510). Subsequently, the switch transmits the data frame onthe determined VC from the outgoing port (operation 1512).

The foregoing descriptions of embodiments of the present invention havebeen presented only for purposes of illustration and description. Theyare not intended to be exhaustive or to limit this disclosure.Accordingly, many modifications and variations will be apparent topractitioners skilled in the art. The scope of the present invention isdefined by the appended claims.

1. A method for facilitating quality of service (QoS) in a Fibre Channel(FC) host bus adaptor (HBA), the method comprising: communicating to anFC switch the HBA's capability of receiving or sending a data flow overa logical channel that couples the HBA to the FC switch; wherein thebandwidth on an FC link between the HBA and the FC switch can beallocated into a plurality of logical channels; wherein a respectivelogical channel can transport data frames of variable length; andwherein a respective logical channel is associated with a dedicatedbuffer; receiving logical-channel allocation information from the FCswitch; associating data frames with a logical channel; and transmittingdata frames to the FC switch on the corresponding logical channel. 2.The method of claim 1, wherein the logical-channel allocationinformation indicates a QoS class to which a respective logical channelbelongs.
 3. The method of claim 1, wherein communicating to the FCswitch the HBA's logical-channel capability comprises: initiating afabric login (FLOGI) process to the FC switch; and transmitting avendor-specific data structure as part of the FLOGI process, wherein thedata structure indicates whether the HBA can receive or send data framesover a logical channel.
 4. The method of claim 1, further comprisingnegotiating with the FC switch a buffer-to-buffer credit for arespective logical channel subsequent to receiving the logical-channelallocation information.
 5. The method of claim 1, wherein prior toreceiving the logical-channel allocation information, the data framescommunicated to the FC switch are transmitted over a default logicalchannel reserved for inter-switch communications.
 6. The method of claim1, further comprising: requesting port assignment from the FC switch;and in response to the request, receiving port assignment from the FCswitch for a physical device or logical entity associated with the HBA.7. The method of claim 6, wherein requesting port assignment from the FCswitch comprises sending the request based on an N_Port IDVirtualization (NPIV) process.
 8. The method of claim 1, furthercomprising transmitting a logical-channel query to the FC switch forinformation indicating association between a logical channel and a dataflow originated from a port within the HBA, wherein the query indicatesa source identifier (S_ID) for the port.
 9. The method of claim 8,wherein transmitting the query to the FC switch comprises addressing thequery to a well-known address in the FC switch.
 10. The method of claim9, wherein the query conforms to the format of an Extended Link Service(ELS) query.
 11. The method of claim 9, wherein the query conforms tothe format of a Fibre Channel Common Transport (FC-CT) query.
 12. Themethod of claim 8, wherein the query indicates a destination to which alogical entity corresponding to the S_ID is to communicate; and whereinthe method further comprises receiving from the FC switch an answerwhich indicates a logical channel assigned to a data flow from thelogical entity associated to the S_ID and the destination identified inthe query.
 13. The method of claim 8, further comprising receiving, inresponse to the query, an answer which indicates a logical channelassigned to a data flow from the logical entity associated to the S_IDto a destination.
 14. The method of claim 8, further comprisingtransmitting a logical-channel query to the FC switch for every portwithin the HBA, thereby allowing data flows originated from differentports within the HBA to be transmitted on different logical channels.15. The method of claim 1, further comprising receiving an update fromthe FC switch, wherein the update indicates a change in the associationbetween the logical channels and QoS classes.
 16. A method forfacilitating quality of service (QoS) in a Fibre Channel (FC) network,the method comprising: receiving a data frame at an FC switch;determining the value of a Class Specific Control (CS_CTL) field in theheader of the data frame; associating the data frame with a logicalchannel based on the CS_CTL value; wherein the bandwidth on an FC linkcan be allocated into a plurality of logical channels; wherein arespective logical channel can transport data frames of variable length;and wherein a respective logical channel is associated with a dedicatedbuffer in the FC switch; and transmitting the data frame on thedetermined logical channel on an outgoing port.
 17. A Fibre Channel (FC)host bus adaptor (HBA) for facilitating quality of service (QoS), theHBA comprising: a link-initialization mechanism configured tocommunicate to an FC switch the HBA's capability of receiving or sendinga data flow over a logical channel that couples the HBA to the FCswitch; wherein the bandwidth on an FC link between the HBA and the FCswitch can be allocated into a plurality of logical channels; wherein arespective logical channel can transport data frames of variable length;and wherein a respective logical channel is associated with a dedicatedbuffer; a logical-channel management mechanism configured to receivelogical-channel allocation information from the FC switch and associatedata frames with a logical channel; and a transmission mechanismconfigured to transmit data frames to the FC switch on the correspondinglogical channel.
 18. The HBA of claim 17, wherein the logical-channelallocation information indicates a QoS class to which a respectivelogical channel belongs.
 19. The HBA of claim 17, wherein whilecommunicating to the FC switch the HBA's logical-channel capability, thelink-initialization mechanism is further configured to: initiate afabric login (FLOGI) process to the FC switch; and transmit avendor-specific data structure as part of the FLOGI process, wherein thedata structure indicates whether the HBA can receive or send data framesover a logical channel.
 20. The HBA of claim 17, further comprising acredit-negotiation mechanism configured to negotiate with the FC switcha buffer-to-buffer credit for a respective logical channel after thelogical-channel allocation information is received.
 21. The HBA of claim17, wherein before the logical-channel allocation information isreceived, the data frames communicated to the FC switch are transmittedover a default logical channel reserved for inter-switch communications.22. The HBA of claim 17, further comprising a port-management mechanismconfigured to: request port assignment from the FC switch; and inresponse to the request, receive port assignment from the FC switch fora physical device or logical entity associated with the HBA.
 23. The HBAof claim 22, wherein while requesting port assignment from the FCswitch, the port-management mechanism is configured to send the requestin an N_Port ID Virtualization (NPIV) process.
 24. The HBA of claim 17,wherein the logical-channel management mechanism is further configuredto transmit a logical-channel query to the FC switch for informationindicating association between a logical channel and a data floworiginated from a port within the HBA, wherein the query indicates asource identifier (S_ID) for the port.
 25. The HBA of claim 24, whereinwhile transmitting the query to the FC switch, the logical-channelmanagement mechanism is configured to address the query to a well-knownaddress in the FC switch.
 26. The HBA of claim 25, wherein the queryconforms to the format of an Extended Link Service (ELS) query.
 27. TheHBA of claim 25, wherein the query conforms to the format of a FibreChannel Common Transport (FC-CT) query.
 28. The HBA of claim 24, whereinthe query indicates a destination to which a logical entitycorresponding to the S_ID is to communicate; and wherein thelogical-channel management mechanism is configured to receive from theFC switch an answer which indicates a logical channel assigned to a dataflow from the logical entity associated to the S_ID and the destinationidentified in the query.
 29. The HBA of claim 24, wherein thelogical-channel management mechanism is further configured to receive,in response to the query, an answer which indicates a logical channelassigned to a data flow from the logical entity associated to the S_IDto a destination.
 30. The HBA of claim 24, wherein the logical-channelmanagement mechanism is configured to transmit a logical-channel queryto the FC switch for every port within the HBA, thereby allowing dataflows originated from different ports within the HBA to be transmittedon different logical channels.
 31. The HBA of claim 17, wherein thelogical-channel management mechanism is further configured to receive anupdate from the FC switch, wherein the update indicates a change in theassociation between the logical channels and QoS classes.
 32. Acomputer-readable medium storing code that represents circuitry whichincludes: communication circuitry to communicate to an FC switch theHBA's capability of receiving or sending a data flow over a logicalchannel that couples the HBA to the FC switch; wherein the bandwidth onan FC link between the HBA and the FC switch can be allocated into aplurality of logical channels; wherein a respective logical channel cantransport data frames of variable length; and wherein a respectivelogical channel is associated with a dedicated buffer; receivercircuitry to receive logical-channel allocation information from the FCswitch; mapping circuitry to associate data frames with a logicalchannel; and transmission circuitry to transmit data frames to the FCswitch on the corresponding logical channel.
 33. A Fibre Channel (FC)network, comprising: an FC switch; a host bus adaptor (HBA); a physicallink coupling the HBA to the FC switch; wherein the bandwidth on thephysical link between the HBA and the FC switch can be allocated into aplurality of logical channels; wherein a respective logical channel cantransport data frames of variable length; wherein a respective logicalchannel is associated with a dedicated buffer; and wherein the HBA isconfigured to: communicate to the FC switch the HBA's capability ofreceiving or sending a data flow over a logical channel that couples theHBA to the FC switch; receive logical-channel allocation informationfrom the FC switch; associate data frames with a logical channel; andtransmit data frames to the FC switch on the corresponding logicalchannel.
 34. A Fibre Channel (FC) switch, comprising: an FC switch; ahost bus adaptor (HBA); a physical link coupling the HBA to the FCswitch; wherein the bandwidth on the physical link between the HBA andthe FC switch can be allocated into a plurality of logical channels;wherein a respective logical channel can transport data frames ofvariable length; wherein a respective logical channel is associated witha dedicated buffer; and wherein the HBA is configured to: communicate tothe FC switch the HBA's capability of receiving or sending a data flowover a logical channel that couples the HBA to the FC switch; receivelogical-channel allocation information from the FC switch; associatedata frames with a logical channel; and transmit data frames to the FCswitch on the corresponding logical channel.
 35. A Fire Channel (FC)switch for facilitating quality of service (QoS) in an FC network, theswitch comprising: a receiving mechanism configured to receive a dataframe at an FC switch; an header-inspection mechanism configured todetermine the value of a Class Specific Control (CS_CTL) field in theheader of the data frame; a logical-channel mapping mechanism configuredto associate the data frame with a logical channel based on the CS_CTLvalue; wherein the bandwidth on an FC link can be allocated into aplurality of logical channels; wherein a respective logical channel cantransport data frames of variable length; and wherein a respectivelogical channel is associated with a dedicated buffer in the FC switch;and a transmission mechanism configured to transmit the data frame onthe determined logical channel on an outgoing port.